1. Field of the Invention
This invention relates to a display device represented by a graphic display device using a fluorescent display tube, and more particularly to such a display device adapted to substantially decrease the number of drive circuit elements and reduce power consumption.
2. Description of the Prior Art
A graphic display device using a fluorescent display tube which has been conventionally known in the art is generally constructed in such a manner as shown in FIG. 5.
More specifically, a fluorescent display tube used in the conventional display device which is generally indicated at reference numeral 1 in FIG. 5 includes a substrate 2 made of an insulating material, on which a plurality of stripe-like anode conductors are arranged. The anode conductors constitute anodes 3 in cooperation with phosphor layers deposited thereon. In the tube of the type wherein its luminous display is observed through the substrate 2, the substrate and anode conductors each are made of a light-permeable material. The fluorescent display tube also includes a front cover 4 arranged opposite to the substrate 2, on which a plurality of filamentary cathodes 6 are stretchedly arranged through cathode supports 5. On the substrate 2 are fixed spacers 7, through which a space is defined between the substrate 2 and the anodes 3. Further, the fluorescent display tube includes a plurality of wire-like control electrodes 8 arranged so as to extend in a direction across the anodes 3. The substrate 2 and front cover 4 are hermetically joined together through side plates 9 to form an envelope, which is evacuated to high vacuum and then an evacuation hole 10 of the envelope is sealedly closed with a lid 11, resulting in the fluorescent display tube 1.
In the fluorescent display tube or device 1 constructed as described above, turning-on of the cathodes 6 for the heating causes them to emit electrons. Also, each intersection between the anodes and the control electrodes arranged across each other constitutes each picture cell. Accordingly, when voltages are selectively applied to the anodes 3 and control electrodes 8 arranged across each other, respectively, electrons emitted from the cathodes 8 impinge on phosphor layers of picture cells selected, resulting in a desired luminous display.
Thus, the conventional fluorescent display tube for the conventional graphic display device generally employs a matrix drive system by means of the anodes and control electrodes. Such a matrix drive system includes a simple matrix system wherein control electrodes are selectively driven one by one and a dual wire scanning system as proposed in Japanese Utility Model Application Laying-Open Publication No. 57-162692 by the assignee wherein a drive signal is concurrently applied to adjacent two control electrodes, so that each anode interposed between the so-selected two control electrodes forms a picture cell. Also, an anode multi-matrix system has been partially put into practice, which is intended to decrease the number of drive circuits on a control electrode side, as disclosed in Japanese Patent Application Laying-Open Publication No. 202050/1982.
Unfortunately, in each of the simple matrix system, dual wire scanning system and anode multi-drive system which are in the category of the matrix drive system, it is required to separately drive the anodes and control electrodes, resulting in an increase in the number of drive circuit elements (hereinafter referred to as "drivers") for the anodes and control electrodes.
More specifically, supposing that, for example, a simple matrix system has 640 picture cells and 400 picture cells arranged in its lateral and longitudinal directions, respectively, or 256,000 (=640.times.400) picture cells in all, it requires 1040 drivers (=640+400).
Accordingly, an increase in the number of picture cells for accomplishing a graphic display of high density leads to an increase in the number of drivers correspondingly, so that costs of circuits for the drivers and costs for manufacturing the device are significantly increased. Also, a graphic display of high density causes a decrease in duty factor, so that an increase in anode voltage is required. Unfortunately, this requires the drivers to withstand a voltage as high as 100 volts to several hundred volts, resulting in a further increase in the costs.
Also, in order to cause all the anodes to carry out a uniform luminous display, the anodes are required to uniformly emit electrons. However, this causes an increase in the number of cathodes, resulting in effective utilization of electrons being deteriorated and power consumption being increased.